Force measurement system having a plurality of measurement surfaces

ABSTRACT

A force measurement assembly includes a first component supported by a first load measuring device and having a first measurement surface; a second component supported by a second load measuring device, spaced apart from the first component by a gap, and having a second measurement surface; and a third load measuring device operatively coupled to both the first component and the second component; wherein the first load measurement device is configured to output at least one first quantity that is representative of the load being applied to the first measurement surface, the second load measurement device is configured to output at least one second quantity that is representative of the load being applied to the second measurement surface, and the third load measuring device is configured to output at least one third quantity that is representative of a load being transferred between the first component and the second component.

CROSS-REFERENCE TO RELATED APPLICATIONS

Not Applicable.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not Applicable.

NAMES OF THE PARTIES TO A JOINT RESEARCH AGREEMENT

Not Applicable.

INCORPORATION BY REFERENCE OF MATERIAL SUBMITTED ON A COMPACT DISK

Not Applicable.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention generally relates to force measurement systems having a plurality of measurement surfaces. More particularly, the invention relates to a force measurement system with two or more measurement surfaces, which is particularly useful in the assessment of the balance of a subject.

2. Background and Description of Related Art

Force measurement systems are utilized in various fields to quantify the reaction forces and moments exchanged between a body and support surface. For example, in biomedical applications, force measurement systems are used for gait analysis, assessing balance and mobility, evaluating sports performance, and assessing ergonomics. In order to quantify the forces and moments resulting from the body disposed thereon, the force measurement system includes some type of force measurement device. Depending on the particular application, the force measurement device may take the form of a balance plate, force plate, jump plate, an instrumented treadmill, or some other device that is capable of quantifying the forces and moments exchanged between the body and the support surface.

A balance assessment of a human subject is frequently performed using a specialized type of a force plate, which is generally known as a balance plate. A balance plate is a sensitive weighing scale, which in addition to measuring the weight of the subject, also measures the point of application of the weight. Typically, this is achieved by having either three or four instrumented feet, each measuring the force transmitted through it. Then, based on how much force each foot carries, the point of application of the total force (i.e., the body weight is calculated). A typical use of a balance plate involves monitoring the manner in which this point of application of the force (i.e., the center of pressure) changes as the subject stands on the plate. For a quietly standing subject, the center of pressure variation is an indication of the amount of physiological sway that the subject experiences. Generally, a small center of pressure variation demonstrates that the subject is essentially stable, whereas a large center of pressure variation in quiet stance is interpreted as an indication that the subject may have difficulty maintaining his or her own balance, and may be in danger of sustaining a fall in normal daily living. Balance plates frequently are used in clinics and assisted-living environments by a clinicians and/or physical therapists who regularly carry the plate from one facility to another. Thus, it is highly desirable for a balance plate to readily portable.

During a balance assessment, if it is desired to make independent measurements under each foot of a subject, two balance plates are typically either placed side-by-side or mounted on a common base. This arrangement permits a determination of the weight that is carried by each leg of the subject, and if there is a deficiency in one of the legs. However, using two separate plates requires carrying additional hardware. Also, the operator has to make sure that the plates are not touching one another as the patient steps on and off the system so that an accurate measurement of each leg can be obtained. When two plates are mounted on one common base, the system becomes significantly heavier, and thus, more difficult to transport. Both conventional two plate systems also have the disadvantage that measurement from each plate is recorded independently, and poses not only an inconvenience, but also increases the possibility of inadvertently mixing the left and right signals.

Also, because many subjects that are tested on a balance plate have a balance disorder or a potential balance problem, it is very important that subjects are able to easily step on and off of the plate. Thus, it is highly desirable for the balance plate to have as low a profile as possible. Although, on a conventional balance plate, the force measuring feet are placed underneath the surface on which the patient stands, which increases the overall height of the instrument and consequently makes it more difficult for a patient having balance disorders to step on and off the plate.

What is needed, therefore, is a force measurement system that is in the form of a single force plate having two or more independent measurement surfaces for assessing the balance of a subject. Moreover, a force measurement system is needed that is readily portable, and thus, easy for an operator to transport from place to place. Furthermore, a need exists for a force measurement system that has a low profile so that it is easier for subjects, such as patients having balance disorders or potential balance problems to step on and off the apparatus.

BRIEF SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to a force measurement system having two or more measurement surfaces that substantially obviates one or more problems resulting from the limitations and deficiencies of the related art.

An object of one or more exemplary embodiments is to provide a force measurement system having two or more measurement surfaces that is readily portable, and does not weigh significantly more than a single force plate used in balance assessment.

Another object of one or more exemplary embodiments is to provide a force measurement system having two or more measurement surfaces with a relatively low profile so as to make it easy for patients to step on and off the plate.

The aforedescribed objects are merely illustrative in nature, and in no way are intended to limit the scope of the claimed invention. Additional objects and advantages of the present invention will be apparent from the following detailed description, the accompanying drawings, and the appended claims.

To achieve one or more of these objects and advantages, in accordance with a first aspect of the present invention, there is provided a dual force plate system having two independent measurement surfaces, which includes: a first plate component having a first measurement surface for receiving a first portion of a body of a subject, a first opposed surface that is disposed generally opposite to the first measurement surface, and a plurality of lateral surfaces that extend between the first measurement surface and the first opposed surface; a second plate component having a second measurement surface for receiving a second portion of the body of the subject, a second opposed surface that is disposed generally opposite to the second measurement surface, and a plurality of lateral surfaces that extend between the second measurement surface and the second opposed surface; a first force transducer element operatively coupled to either the first opposed surface of the first plate component or to one of the lateral surfaces of the first plate component, the first force transducer element configured to output at least one first quantity that is representative of a load being applied to the first measurement surface; a second force transducer element operatively coupled to either the second opposed surface of the second plate component or to one of the lateral surfaces of the second plate component, the second force transducer element configured to output at least one second quantity that is representative of a load being applied to the second measurement surface; and a third force transducer element operatively coupled to either the first opposed surface of the first plate component and the second opposed surface of the second plate component, or to one of the lateral surfaces of the first plate component and one of lateral surfaces of second plate component, the third force transducer element configured to output at least one third quantity that is representative of a load being transferred between the first plate component and the second plate component.

In a preferred embodiment of this aspect of the present invention, either the first and third force transducer elements are both operatively coupled to the first opposed surface of the first plate component, or the first and third force transducer elements are both operatively coupled to the same lateral side of the first plate component.

In another preferred embodiment, either the second and third force transducer elements are both operatively coupled to the second opposed surface of the second plate component, or the second and third force transducer elements are both operatively coupled to the same lateral side of the second plate component.

In yet another preferred embodiment, the dual force plate system further comprises a fourth force transducer element laterally spaced apart from the first force transducer element, the fourth force transducer element operatively coupled to either the first opposed surface of the first plate component or to another one of the lateral surfaces of the first plate component, the fourth force transducer element configured to output at least one fourth quantity that is representative of a load being applied to the first measurement surface; a fifth force transducer element laterally spaced apart from the second force transducer element, the fifth force transducer element operatively coupled to either the second opposed surface of the second plate component or to another one of the lateral surfaces of the second plate component, the fifth force transducer element configured to output at least one fifth quantity that is representative of a load being applied to the second measurement surface; and a sixth force transducer element laterally spaced apart from the third force transducer element, the sixth force transducer element operatively coupled to either the first opposed surface of the first plate component and the second opposed surface of the second plate component, or to another one of the lateral surfaces of the first plate component and another one of lateral surfaces of second plate component, the sixth force transducer element configured to output at least one sixth quantity that is representative of a load being transferred between the first plate component and the second plate component.

In still another preferred embodiment, the first, second, and third force transducer elements are generally symmetrically arranged with respect to the fourth, fifth, and sixth force transducer elements.

In yet another preferred embodiment, the first force transducer element, the second force transducer element, and the third force transducer element are each part of a continuous beam force transducer assembly, the first, second and third force transducer elements being spaced apart along the length of the continuous beam force transducer assembly; and wherein the continuous beam force transducer assembly extends substantially the combined length of the first and second opposed surfaces of the first and second plate components, or the combined length of the lateral surfaces of the first and second plate components to which the first and second force transducer elements are respectively coupled.

In still another preferred embodiment, the first force transducer element is in the form of a first discrete transducer beam, the second force transducer element is in the form of a second discrete transducer beam, and the third force transducer element is in the form of a third discrete transducer beam; wherein the first and third discrete transducer beams are spaced apart from the second discrete transducer beam in a longitudinal direction thereof; and wherein the first, second, and third discrete transducer beams are disposed in a spaced apart relationship along the first and second opposed surfaces of the first and second plate components, or along two adjacent lateral surfaces of the first and second plate components.

In yet another preferred embodiment, the first force transducer element is mounted in a cantilevered manner from the first plate component and the second force transducer element is mounted in a cantilevered manner from the second plate component.

In still another preferred embodiment, the dual force plate system further comprises a data processing device operatively coupled to the first force transducer element, the second force transducer element, and the third force transducer element, the data processing device configured to receive the first, second, and third quantities that are representative of the loads being applied to the first measurement surface, the second measurement surface, and transferred between the first and second plate components, respectively, and to convert the first, second, and third quantities into output loads.

In yet another preferred embodiment, the first force transducer element, the second force transducer element, and the third force transducer element each comprise an aperture disposed therein and a plurality of strain gages disposed on an outer surface thereof, the outer surface of each force transducer element on which the plurality of strain gages are disposed being generally opposite to an inner surface of each aperture.

In still another preferred embodiment, a support foot having a longitudinal axis is disposed on both the first force transducer element and the second force transducer element, the longitudinal axis of each support foot being disposed substantially perpendicular to the extending direction of a respective aperture in the first force transducer element and the second force transducer element.

In yet another preferred embodiment, the third force transducer element further comprises an additional plurality of strain gages disposed on opposed outer surfaces thereof for sensing mechanical strain resulting from both tension and compression.

In still another preferred embodiment, the first force transducer element and the second force transducer element each have a protruding portion disposed on an outer surface thereof, and wherein the first and second force transducer elements are respectively coupled to the first and second plate components by means of their respective protruding portions.

In yet another preferred embodiment, the third force transducer element has first and second protruding portions disposed on an outer surface thereof, the first protruding portion being operatively coupled to the first opposed surface of the first plate component, the second protruding portion being spaced apart from the first protruding portion and being operatively to the second opposed surface of the second plate component.

In still another preferred embodiment, the lateral side of the first plate component to which the first force transducer element is operatively coupled, and the lateral side of the second plate component to which the second force transducer element is operatively coupled, each have a centrally disposed protruding portion; and wherein the first force transducer element is operatively coupled to the centrally disposed protruding portion of the first plate component, and the second force transducer element is operatively coupled to the centrally disposed protruding portion of the second plate component.

In yet another preferred embodiment, the third force transducer element is operatively coupled to the centrally disposed protruding portion of the first plate component and the centrally disposed protruding portion of the second plate component.

In still another preferred embodiment, the first plate component and second plate component are both constructed from a material or a composite structure having a high stiffness value such that the natural frequency of the dual force plate system is maximized and the first and second plate components are capable of withstanding the weight of the subject.

In yet another preferred embodiment, a gap is provided between the first plate component and the second plate component so as to prevent interaction between the two plate components.

In still another preferred embodiment, the first force transducer element and the second force transducer element each comprise an elastically deformable structural member and a plurality of strain gages, the strain gages being used to measure the deformation of the elastically deformable structural member due to shear.

In yet another preferred embodiment, the third force transducer element comprises an elastically deformable structural member, a first plurality of strain gages disposed on a first side of the elastically deformable structural member, and a second plurality of strain gages disposed on a second side of the elastically deformable structural member that is opposite to the first side, the first and second pluralities of strain gages being used to measure the deformation of the elastically deformable structural member due to bending.

In accordance with a second aspect of the present invention, there is provided a dual force plate system having two independent measurement surfaces, which includes: a first plate component having a first measurement surface for receiving a first portion of a body of a subject, a first opposed surface that is disposed generally opposite to the first measurement surface, and a plurality of lateral surfaces that extend between the first measurement surface and the first opposed surface; a second plate component having a second measurement surface for receiving a second portion of the body of the subject, a second opposed surface that is disposed generally opposite to the second measurement surface, and a plurality of lateral surfaces that extend between the first measurement surface and the second opposed surface; a first force transducer element operatively coupled to either the first opposed surface of the first plate component or to one of the lateral surfaces of the first plate component, the first force transducer element configured to output at least one first quantity that is representative of a load being applied to the first measurement surface; a second force transducer element operatively coupled to either the second opposed surface of the second plate component or to one of the lateral surfaces of the second plate component, the second force transducer element configured to output at least one second quantity that is representative of a load being applied to the second measurement surface; a third force transducer element operatively coupled to either the first opposed surface of the first plate component and the second opposed surface of the second plate component, or to one of the lateral surfaces of the first plate component and one of lateral surfaces of second plate component, the third force transducer element configured to output at least one third quantity that is representative of a load being transferred between the first plate component and the second plate component; and a data processing device operatively coupled to the first force transducer element, the second force transducer element, and the third force transducer element, the data processing device configured to receive the first, second, and third quantities that are representative of the loads being applied to the first measurement surface, the second measurement surface, and transferred between the first and second plate components, respectively, and to convert the first, second, and third quantities into output loads.

In accordance with a third aspect of the present invention, there is provided a force measurement assembly having two measurement surfaces, which includes: a first component having a first measurement surface configured to receive a first portion of a body of a subject or a first object exerting a load thereon, the first component being structurally supported by a first load measuring device; a second component having a second measurement surface configured to receive a second portion of the body of the subject or a second object exerting a load thereon, the second component being structurally supported by a second load measuring device and being spaced apart from the first component by a gap; and a third load measuring device operatively coupled to both the first component and the second component; wherein the first load measurement device is configured to output at least one first quantity that is representative of the load being applied to the first measurement surface, the second load measurement device is configured to output at least one second quantity that is representative of the load being applied to the second measurement surface, and the third load measuring device is configured to output at least one third quantity that is representative of a load being transferred between the first component and the second component.

In accordance with a fourth aspect of the present invention, there is provided a force plate system having three or more independent measurement surfaces, which includes: a first outer plate component having a first measurement surface, a first opposed surface that is disposed generally opposite to the first measurement surface, and a plurality of lateral surfaces that extend between the first measurement surface and the first opposed surface; a second outer plate component having a second measurement surface, a second opposed surface that is disposed generally opposite to the second measurement surface, and a plurality of lateral surfaces that extend between the second measurement surface and the second opposed surface; one or more inner plate components that are disposed between the first outer plate component and the second outer plate component, each inner plate component having a measurement surface, an opposed surface that is disposed generally opposite to the measurement surface, and a plurality of lateral surfaces that extend between the measurement surface and the opposed surface; a first outer force transducer element operatively coupled to either the first opposed surface of the first outer plate component or to one of the lateral surfaces of the first outer plate component, the first outer force transducer element configured to output at least one first quantity that is representative of a load being applied to the first measurement surface; a second outer force transducer element operatively coupled to either the second opposed surface of the second outer plate component or to one of the lateral surfaces of the second outer plate component, the second outer force transducer element configured to output at least one second quantity that is representative of a load being applied to the second measurement surface; and a plurality of inner force transducer elements operatively coupling the one or more inner plate components to either the first and second opposed surfaces of the first and second outer plate components, or to lateral surfaces of the first and second outer plate components, the plurality of inner forces transducer elements configured to output a plurality of quantities that are representative of loads being transferred between the one or more inner plate components and the first and second outer plate components.

It is to be understood that the foregoing objects and summary, and the following detailed description of the present invention, are merely exemplary and explanatory in nature. As such, the foregoing objects and summary, and the following detailed description of the invention, should not be construed to limit the scope of the appended claims in any sense.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The invention will now be described, by way of example, with reference to the accompanying drawings, in which:

FIG. 1 is a perspective view of a dual force plate system according to a first embodiment of the invention;

FIG. 2 is a perspective view of a dual force plate assembly of the dual force plate system according to the first embodiment of the invention;

FIG. 3 is a cut-away sectional view of the dual force plate assembly of the dual force plate system according to the first embodiment of the invention;

FIG. 4 is a side view of the dual force plate assembly of the dual force plate system according to the first embodiment of the invention;

FIG. 5 is a top view of the dual force plate assembly of the dual force plate system according to the first embodiment of the invention;

FIG. 6 is a bottom view of the dual force plate assembly of the dual force plate system according to the first embodiment of the invention;

FIG. 7 is an enlarged, cut-away sectional view of a force transducer element of the dual force plate assembly according to the first embodiment of the invention, which depicts the placement of a strain gage thereon;

FIG. 8 is a block diagram illustrating a data acquisition/data processing system utilized in the embodiments of the force plate systems described herein;

FIG. 9 is a perspective view of a dual force plate assembly of the dual force plate system according to a second embodiment of the invention;

FIG. 10 is a cut-away sectional view of the dual force plate assembly of the dual force plate system according to the second embodiment of the invention;

FIG. 11 is a side view of the dual force plate assembly of the dual force plate system according to the second embodiment of the invention;

FIG. 12 is a perspective view of a dual force plate assembly of the dual force plate system according to a third embodiment of the invention;

FIG. 13 is a top view of the dual force plate assembly of the dual force plate system according to the third embodiment of the invention;

FIG. 14 is a perspective view of a dual force plate assembly of the dual force plate system according to a fourth embodiment of the invention;

FIG. 15 is a top view of the dual force plate assembly of the dual force plate system according to the fourth embodiment of the invention;

FIG. 16 is a side view of a triple force plate assembly of a triple force plate system according to a fifth embodiment of the invention;

FIG. 17A is a side view of a dual force plate assembly of a dual force plate system according to an exemplary embodiment of the invention with exemplary applied forces depicted thereon so as to illustrate the manner in which the x-coordinates of the center-of-pressure are determined;

FIG. 17B is a free body diagram that diagrammatically represents the forces and moments acting on the dual force plate assembly according to the exemplary embodiment of the invention;

FIG. 17C is a shear diagram that diagrammatically represents the shear forces acting on the dual force plate assembly according to the exemplary embodiment of the invention;

FIG. 17D is a moment diagram that diagrammatically represents the moments acting on the dual force plate assembly according to the exemplary embodiment of the invention; and

FIG. 18 is three-dimensional (3-D) free body diagram/shear diagram that diagrammatically represents the forces acting on the dual force plate assembly according to the exemplary embodiment of the invention so as to illustrate the manner in which the y-coordinates of the center-of-pressure are determined.

Throughout the figures, the same parts are always denoted using the same reference characters so that, as a general rule, they will only be described once.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION A. First Embodiment

A first embodiment of a dual force plate system is seen generally at 100 in FIG. 1. The dual force plate system 100 generally comprises a dual force plate assembly 102 operatively coupled to a data acquisition/data processing device 104 by virtue of an electrical cable 126. In the first embodiment, the dual force plate assembly 102 for receiving a subject utilizes a continuous force transducer beam design. In a preferred embodiment of the invention, the electrical cable 126 is used for data transmission, as well as for providing power to the dual force plate assembly 102. Preferably, the electrical cable 126 contains a plurality of electrical wires bundled together, with at least one wire being used for power and at least another wire being used for transmitting data. The bundling of the power and data transmission wires into a single electrical cable 126 advantageously creates a simpler and more efficient design. In addition, it enhances the safety of the testing environment when human subjects are being tested on the dual force plate assembly 102. However, it is to be understood that the dual force plate assembly 102 can be operatively coupled to the data acquisition/data processing device 104 using other signal transmission means, such as a wireless data transmission system. If a wireless data transmission system is employed, it is preferable to provide the dual force plate assembly 102 with a separate power supply in the form of an internal power supply or a dedicated external power supply.

Referring again to FIG. 1, it can be seen that the dual force plate assembly 102 according to the first embodiment of the invention, includes a first plate component 106, a second plate component 108, and continuous force transducer beams 110 a, 110 b mounted on opposite lateral sides of the first plate component 106 and second plate component 108. As depicted in FIG. 1, the continuous force transducer beams 110 a, 110 b extend substantially the combined width of the first plate component 106 and second plate component 108. Each continuous force transducer beam 110 a, 110 b includes a plurality of force transducer elements 112 a, 112 b, 112 c disposed along the length thereof. The first plate component 106 has a top surface 114 that is configured to receive a first portion of a body of a subject. Similarly, the second plate component 108 has a top surface 116 that is configured to receive a second portion of a body of a subject. In a preferred embodiment, a subject stands in an upright position on the dual force plate assembly 102 and each foot of the subject is placed on the top surfaces 114, 116 of a respective plate component 106, 108 (i.e., one foot on the top surface 114 of the first plate component 106 and the other foot on the top surface 116 of the second plate component 108).

As shown in FIG. 1, the data acquisition/data processing device 104 (e.g., in the form of a laptop digital computer) generally includes a base portion 118 with a central processing unit (CPU) disposed therein for collecting and processing the data that is received from the dual force plate assembly 102, and a plurality of devices 120-124 operatively coupled to the central processing unit (CPU) in the base portion 118. Preferably, the devices that are operatively coupled to the central processing unit (CPU) comprise user input devices 120, 124 in the form of a keyboard 120 and a touchpad 124, as well as a graphical user interface in the form of a laptop LCD screen 122. While a laptop type computing system is depicted in FIG. 1, one of ordinary skill in the art will appreciate that another type of data acquisition/data processing device 104 can be substituted for the laptop computing system such as, but not limited to, a palmtop computing device (i.e., a PDA) or a desktop type computing system having a plurality of separate, operatively coupled components (e.g., a desktop type computing system including a main housing with a central processing unit (CPU) and data storage devices, a remote monitor, a remote keyboard, and a remote mouse). In addition, rather than providing a data acquisition/data processing device 104, it is to be understood that, in other embodiments, only a data acquisition device could be provided without departing from the spirit and the scope of the claimed invention.

Now, turning to FIGS. 2-4, the dual force plate assembly 102 will now be described in more detail. As described above, the dual force plate assembly 102 includes a first plate component 106 with a top surface 114 and a second plate component 108 with a top surface 116. A narrow gap 128 is provided between the first plate component 106 and the second plate component 108 so as to prevent interaction between the two plate components 106, 108. In a preferred embodiment, the narrow gap is between approximately 2 mm and approximately 3 mm, and more preferably, between 2 mm and 3 mm. As best shown in FIGS. 2 and 3, the gap 128 is continuous and completely separates the first plate component 106 from the second plate component 108 (i.e., the plate components 106, 108 do not contact one another at any location along the gap 128). In a preferred embodiment of the invention, the first and second plate components 106, 108 have a composite structure that includes an inverted top tray, structural steel members disposed inside the tray, and a metallic bottom sheet (e.g., an aluminum sheet). Alternatively, the first and second plate components 106, 108 could be provided with a composite structure that utilizes an aluminum honeycomb core inside the inverted top tray, rather than the structural steel members. In this variant of the invention, the honeycomb core is secured to the top tray and the bottom aluminum sheet using a metallic adhesive. This design allows the surface to be very stiff without adding excessive weight. In another variant of the invention, the first and second plate components 106, 108 are formed from a solid plate of material (e.g., a solid aluminum plate or a solid steel plate) with a high stiffness value. Regardless of the precise manner in which the first and second plate components 106, 108 are formed, it is highly desirable for the plate components 106, 108 to have a high stiffness value so as to ensure the structural integrity of the dual force plate assembly 102 when a subject having a substantial weight is disposed thereon. In an exemplary embodiment, the dual force plate assembly 102 is designed to have a natural frequency of at least 100 Hz and is capable of withstanding a subject weight of up to 2,225 Newtons (500 lbs.).

Advantageously, in a preferred embodiment, the dual force plate system 100, which includes dual force plate assembly 102, utilizes substantially the same number of components as a single force plate used in balance assessment.

Referring to FIGS. 2 and 4, it can be seen that each continuous force transducer beam 110 a, 110 b is attached to the underside of the first and second plate components 106, 108. In particular, as best shown in FIGS. 3 and 4, it can be seen that the top surface of each continuous force transducer beam 110 a, 110 b is provided with two protruding portions 142 a, 142 b. The protruding portions 142 a, 142 b are spaced apart from one another along the length of each continuous force transducer beam 110 a, 110 b. The top surface of the first protruding portion 142 a on each of the continuous force transducer beams 110 a, 110 b is fixedly attached to the bottom surface of the first plate component 106, whereas the top surface of the second protruding portion 142 b on each of the continuous force transducer beams 110 a, 110 b is fixedly attached to the bottom surface of the second plate component 108. It is highly advantageously that the first and second plate components 106, 108 only be connected to the protruding portions 142 a, 142 b of the continuous force transducer beams 110 a, 110 b so as to ensure that the total load applied to the top surfaces 114, 116 of the plate components 106, 108 is only transmitted through the force transducer elements 112 a, 112 b, 112 c. Each force transducer beam 110 a, 110 b can be fixedly attached to each plate component 106, 108 by utilizing a plurality of different attachment means such as, but not limited to, threaded fasteners (e.g., screws) or different types of suitable adhesives (e.g., an adhesive designed for bonding metallic components to one another).

As best illustrated in FIGS. 5 and 6, each force transducer beam 110 a, 110 b is provided with respective support feet 134 c, 134 d and 134 a, 134 b disposed at opposed longitudinal ends thereof. In the illustrated embodiment, the first of the two transducer beams 110 a is provided with one non-adjustable support foot 134 c near a first longitudinal end thereof and one adjustable support foot 134 d near the other longitudinal end thereof, while the second of the two force transducer beams 110 b is provided with two (2) non-adjustable support feet 134 a, 134 b disposed at opposed longitudinal ends thereof. The dual force plate assembly 102 is designed to be installed on a floor of a building or on any other rigid surface. The adjustable support foot 134 d facilitates the leveling of the dual force plate assembly 102 on an uneven surface.

Referring again to FIGS. 5 and 6, the dual force plate assembly 102 is provided with a preamplifier board 136 mounted to the underside of the second plate component 108. As diagrammatically illustrated in FIG. 6, the preamplifier board 136 is operatively coupled to the pluralities of strain gages 138 a-138 e via a network of electrical wiring 132. In the depicted embodiment, the preamplifier board 136 is provided with a port 130 for receiving the end of the electrical cable 126 that operatively couples the force plate assembly 102 to the a data acquisition/data processing device 104. The preamplifier board 136 is used to increase the magnitudes of the transducer analog voltages, and preferably, to convert the analog voltage signal(s) into digital voltage signal(s) as well. Advantageously, the preamplifier 136 is placed in close proximity to the two sets of force transducer elements 112 a-112 c in order to amplify the output voltage signal(s) before they are degraded by the effects of noise and interference while being transmitted over the substantial distance from the dual force plate assembly 102 to the data acquisition/data processing device 104. While the preamplifier board 136 is depicted as being mounted on the underside of the second plate component 108 in the illustrated embodiment of the invention, it is to be understood that, in other embodiments of the invention, the preamplifier board 136 could be alternatively mounted on the underside of the first plate component 106 or could be provided in the form of a standalone unit. Also, in yet another embodiment, an analog voltage signal(s) could be outputted from the preamplifier board 136 and then, subsequently converted to a digital voltage signal(s) at the data acquisition/data processing device 104.

In the cut-away sectional view illustrated in FIG. 3, it can be seen that the first of the two transducer beams 110 a is provided with three force transducer elements 112 a, 112 b, 112 c disposed along the length thereof. The first transducer element 112 a is disposed at a first longitudinal end of the first transducer beam 110 a. In a preferred embodiment of the invention, the first transducer element 112 a comprises a longitudinal segment of the force transducer beam 110 a, an aperture 136 a disposed through the longitudinal segment of the force transducer beam 110 a, and a plurality of strain gages 138 a secured to the outer, top surface of the longitudinal segment of the force transducer beam 110 a and substantially centered on the aperture 136 a. The outer, top surface of the first transducer element 112 a on which the plurality of strain gages 138 a is disposed are generally opposite to the inner top surface of the aperture 136 a. When a load is applied to the first plate component 106, the load is transferred to the longitudinal segment of the force transducer beam 110 a that is associated with the first transducer element 112 a, which operates as an elastically deformable structural member. The plurality of strain gages 138 a is used to measure the deformation of the elastically deformable structural member (i.e., the longitudinal segment of the force transducer beam 110 a) resulting from the shear forces imparted on the member from the applied load. While in a preferred embodiment, the longitudinal segment of the force transducer beam 110 a is provided with the aperture 136 a therein to maximize the shear effect when the load is applied to the first plate component 106 by reducing the cross-sectional area of the beam 110 a at the location of the aperture 136 a, it is to be understood that the invention is not so limited. Rather, in other embodiments of the invention, the longitudinal segment of the force transducer beam 110 a, which forms a component of the first transducer element 112 a, is not provided with an aperture disposed therein.

As shown in FIG. 3, the second transducer element 112 b is disposed in a central region of the force transducer beam 110 a. Similar to the first transducer element 112 a, the second transducer element 112 b comprises a longitudinal segment of the force transducer beam 110 a, an aperture 136 b disposed through the longitudinal segment of the force transducer beam 110 a, and a plurality of strain gages 138 b secured to the outer, top surface of the longitudinal segment of the force transducer beam 110 a and substantially centered on the aperture 136 b. Also, as with the first transducer element 112 a, the outer, top surface of the second transducer element 112 b on which the plurality of strain gages 138 b is mounted is oriented generally opposite to the inner top surface of the aperture 136 b. However, unlike the first transducer element 112 a, the second transducer element 112 b also contains two additional pluralities of strain gages 138 c, 138 d mounted thereon for measuring the bending imparted on second transducer element 112 b by a load applied to first plate component 106 and second plate component 108 (see FIGS. 3 and 6). The first additional plurality of strain gages 138 c is mounted on the outer, top surface of the second transducer element 112 b, horizontally spaced apart from the plurality of strain gages 138 b. The second additional plurality of strain gages 138 d is mounted on the outer, bottom surface of the second transducer element 112 b, and is substantially vertically aligned with the first additional plurality of strain gages 138 c (see FIG. 6). When the second transducer element 112 b undergoes bending due to the application of a load on plate components 106, 108, the first additional plurality of strain gages 138 c is configured to measure the deformation of the segmental portion of the force transducer beam 110 a due to compression, while the second additional plurality of strain gages 138 d is configured to measure the deformation of the segmental portion of the force transducer beam 110 a due to tension. The shear force measurement performed by the plurality of strain gages 138 b is analogous to that described above for the plurality of strain gages 138 a of the first transducer element 112 a. In addition, as described above for the first transducer element 112 a, the aperture 136 b is omitted from the second transducer element 112 b in some embodiments of the invention.

Referring again to FIG. 3, it can be seen that a third transducer element 112 c is disposed at a second longitudinal end of the first transducer beam 110 a, which is opposite to its first longitudinal end on which the first transducer element 112 a is disposed. In other words, the third transducer element 112 c is generally in a mirrored relationship with respect to the first transducer element 112 a. Like the first transducer element 112 a, the third transducer element 112 c comprises a longitudinal segment of the force transducer beam 110 a, an aperture 136 c disposed through the longitudinal segment of the force transducer beam 110 a, and a plurality of strain gages 138 e secured to the outer, top surface of the longitudinal segment of the force transducer beam 110 a and substantially centered on the aperture 136 c. The third transducer element 112 c functions in the same manner as described above for the first transducer element 112 a, except that the third transducer element 112 c measures the shear force resulting from a load being applied to the second plate component 108, rather than the first plate component 106.

As shown in FIGS. 2-4, a second force transducer beam 110 b is mounted on a side of the bottom surface of the first and second plate components 106, 108 that is opposite to the side of the bottom surface on which the first force transducer beam 110 a is mounted. The second force transducer beam 110 b is generally a mirror image of the first force transducer beam 110 a. Like the first force transducer beam 110 a, the second force transducer beam 110 b contains first, second, and third force transducer elements 112 a, 112 b, 112 c with respective apertures 136 a, 136 b, 136 c disposed along the length thereof and pluralities of strain gages 138 a-138 e.

FIG. 7 depicts an enlarged view of force transducer element 112 c. While the force transducer elements 112 a, 112 b, 112 c shown in the drawings are beam-type force transducers, which have a generally elongated shape, one of ordinary skill in the art will appreciate that the present invention can be practiced with other types of force transducers such as, but not limited to, pylon-type force transducers. Typically, pylon-type force transducers have a plurality of strain gages adhered to the outer periphery of a cylindrically-shaped force transducer sensing element. In such a case, the force transducer elements 112 a, 112 c, which are disposed at opposite corners of the first and second plate components 106, 108, would be replaced with four (4) pylon-type force transducers disposed at each of the four (4) corners of the dual force plate assembly 102 (i.e., one (1) at each of the outer two corners of first plate component 106 and one (1) at each of the outer two corners of second plate component 108). In such an alternative arrangement, two force transducer elements, which are similar to force transducer elements 112 b, would still be required for measuring the load transferred between the first plate component 106 and the second plate component 108.

FIG. 8 graphically illustrates the acquisition and processing of the load data carried out by the dual force plate system 100. Initially, as shown in FIG. 8, a load L is applied to the dual force plate assembly 102 by a subject disposed thereon. The load is transmitted from the first and second plate components 106, 108 to the two sets of force transducer elements 112 a-112 c. In a preferred embodiment of the invention, each of the force transducer elements 112 a, 112 c includes a plurality of strain gages wired in a Wheatstone bridge configuration, wherein the electrical resistance of each strain gage is altered when the associated longitudinal segment of the associated force transducer beam 110 a, 110 b undergoes deformation resulting from the load (i.e., forces and/or moments) acting on the first and second plate components 106, 108. In a preferred embodiment, the centrally-disposed force transducer elements 112 b each include two (2) pluralities of strain gages wired in a Wheatstone bridge configuration, one for measuring shear and the other for measuring bending. Alternatively, rather than measuring both the shear force and bending moment, each centrally disposed transducer element 112 b can measure a first bending moment at a first location along the length of the transducer element 112 b and a second bending moment at a second location along the length of the transducer element 112 b, the first location being spaced apart from the second location. For each plurality of strain gages disposed on the force transducer elements 112 a-112 c, the change in the electrical resistance of the strain gages brings about a consequential change in the output voltage of the Wheatstone bridge (i.e., a quantity representative of the load being applied to the measurement surface). Thus, the two sets of outer force transducer elements 112 a, 112 c transmit a total of four (4) analog output voltages (signals) to the preamplifier board 136, and the two centrally-disposed force transducer elements 112 b also transmit a total of four (4) analog output voltages (signals) to the preamplifier board 136. As described above, the preamplifier board 136 is used to increase the magnitudes of the transducer analog voltages, and preferably, to convert the analog voltage signals into digital voltage signals as well. After which, the dual force plate assembly 102 transmits the force plate output signals S_(FPO1)-S_(FPO8) to a main signal amplifier/converter 140. Depending on whether the preamplifier board 136 also includes an analog-to-digital (A/D) converter, the force plate output signals S_(FPO1)-S_(FPO8) could be either in the form of analog signals or digital signals. The main signal amplifier/converter 140 further magnifies the force plate output signals S_(FPO1)-S_(FPO8), and if the signals S_(FPO1)-S_(FPO8) are of the analog-type (for a case where the preamplifier board 136 did not include an analog-to-digital (A/D) converter), it may also convert the analog signals to digital signals. Then, the signal amplifier/converter 140 transmits either the digital or analog signals S_(ACO1)-S_(ACO8) to the data acquisition/data processing device 104 so that the forces and/or moments that are being applied to the surfaces of the dual force plate assembly 102 can be outputted to a user (i.e., the output load OL). In addition to a computer, which generally includes a central processing unit (CPU) in a base portion 118, a graphical user interface 122, and a plurality of user input devices 120, 124, the data acquisition/data processing device 104 may further comprise an analog-to-digital (A/D) converter if the signals S_(ACO1)-S_(ACO8) are in the form of analog signals. In such a case, the analog-to-digital converter will convert the analog signals into digital signals for processing by a central processing unit (CPU).

When the data acquisition/data processing device 104 receives the voltage signals S_(ACO1)-S_(ACO8), it transforms the signals into output forces and/or moments by multiplying the voltage signals S_(ACO1)-S_(ACO8) by a calibration matrix. After which, the force F_(L) exerted on the surface of the first force plate by the left foot of the subject, the force F_(R) exerted on the surface of the second force plate by the right foot of the subject, and the center of pressure for each foot of the subject (i.e., the x and y coordinates of the point of application of the force applied to the measurement surface by each foot) are determined by the data acquisition/data processing device 104. The computations performed in the determination of the forces and center of pressure are described hereinafter.

While, in a preferred embodiment of the invention, the data acquisition/data processing device 104 determines the forces F_(L), F_(R) exerted on the surface of the first and second force plates by the feet of the subject and the center of pressure for each foot of the subject, it is to be understood that the invention is not so limited. Rather, in other embodiments of the invention, the output forces of the data acquisition/data processing device 104 could include all three (3) orthogonal components of the resultant forces acting on the two plate components 106, 108. In yet other embodiments of the invention, the output forces and moments of the data acquisition/data processing device 104 can be in the form of other forces and moments as well.

B. Second Embodiment

A second embodiment of the dual force plate assembly is seen generally at 202 in FIG. 9. In accordance with the second embodiment of the invention, a dual force plate system generally comprises the dual force plate assembly 202 of FIG. 9 operatively coupled to a data acquisition/data processing device 104 by virtue of an electrical cable 126 (as illustrated in FIG. 1 for the dual force plate assembly 102). In the second embodiment, the dual force plate assembly 202 for receiving a subject utilizes a plurality of spaced apart, short transducer beams 208, 210, 212 disposed underneath, and near opposite lateral sides of, a first plate component 204 and a second plate component 206. Because the data acquisition/data processing device 104 and the electrical cable 126 are the same as that described above with regard to the first embodiment, a description of these components 104, 126 will not be repeated for this embodiment. Like the dual force plate assembly 102 of the first embodiment, the dual force plate assembly 202 also includes a preamplifier board (not explicitly shown in FIG. 9) mounted to the underside of the second plate component 206. In addition, similar to the preceding embodiment, the preamplifier board is provided with a port 220 for receiving the end of the electrical cable 126 that operatively couples the force plate assembly 202 to the data acquisition/data processing device 104.

Advantageously, the use of three discrete transducer beams 208, 210, 212 on each side of the dual force plate assembly 202, rather two continuous beams on each side thereof, reduces the overall amount of stock materials that are required in the fabrication of the plate assembly 202. This is particularly important for dual force plate assemblies that have a large footprint.

As illustrated in FIG. 9, the dual force plate assembly 202 according to the second embodiment of the invention includes a first plate component 204, a second plate component 206, and two sets of spaced apart, short transducer beams 208, 210, 212 disposed underneath, and near opposite lateral sides of, the first plate component 204 and second plate component 206. As depicted in FIG. 9, the first short transducer beam 208 is disposed in a first corner of the dual force plate assembly 202 and includes a first force transducer element 218 a. The second short transducer beam 210 is connected to both the first plate component 204 and the second plate component 206 and comprises a second force transducer element 218 b, while the third short transducer beam 212 is disposed in a second corner of the dual force plate assembly 202 and includes a third force transducer element 218 c. As in the first embodiment, the first plate component 204 has a top surface 214 that is configured to receive a first portion of a body of a subject. Similarly, the second plate component 206 has a top surface 216 that is configured to receive a second portion of a body of a subject. Also, similar to the first embodiment described above, a narrow gap 224 is provided between the first plate component 204 and the second plate component 206 so as to prevent interaction between the two plate components 204, 206.

Because the short transducer beams 208, 210, 212 disposed underneath, and near opposite lateral sides of, the first plate component 204 and second plate component 206 are structurally identical to one another, only one set of force transducer beams 208, 210, 212 will be described with regard to the second embodiment. As depicted in FIGS. 10 and 11, each short transducer beam 208 has a top protruding portion 236 that is fixedly attached to the bottom surface of the first plate component 204. Similarly, each oppositely disposed, short transducer beam 212 has a top protruding portion 242 that is fixedly attached to the bottom surface of the second plate component 206. Each centrally disposed short transducer beam 210, each of which extends below the gap 224, comprises a first protruding portion 238 that is fixedly attached to the bottom surface of the first plate component 204 and a second protruding portion 240 that is fixedly attached to the bottom surface of the second plate component 206. Similar to the first embodiment described above, the short transducer beams 208, 210, 212 comprise respective transducer elements 218 a, 218 b, 218 c (which are formed by respective longitudinal segments of the force transducer beams 208, 210, 212) and respective apertures 226 a, 226 b, 226 c disposed therethrough. Also, as in the first embodiment, the outer transducer elements 218 a, 218 c measure the shear forces exerted on the first and second plate components 204, 206, respectively, whereas the centrally disposed transducer elements 218 b measure both the shear force and bending moment resulting from a load being applied to the first and second plate components 204, 206. Alternatively, rather than measuring both the shear force and bending moment, each centrally disposed transducer element 218 b can measure a first bending moment at a first location along the length of the transducer element 218 b and a second bending moment at a second location along the length of the transducer element 218 b, the first location being spaced apart from the second location.

Like the force transducer element 112 a described with regard to the first embodiment of the invention, the force transducer element 218 a is provided with a plurality of strain gages 234 a secured to the outer, top surface of the longitudinal segment of the force transducer beam 208 and substantially centered on the aperture 226 a (see FIG. 10). Also, similar to the force transducer element 112 c of the first embodiment, the force transducer element 218 c is provided with a plurality of strain gages 234 d secured to the outer, top surface of the longitudinal segment of the force transducer beam 212 and substantially centered on the aperture 226 c. In addition, like the force transducer element 112 b of the first embodiment of the invention, the force transducer element 218 b is provided with a plurality of strain gages 234 b secured to the outer, top surface of the longitudinal segment of the force transducer beam 210 and substantially centered on the aperture 226 b, a first additional plurality of strain gages 234 c mounted on the outer, top surface of the second transducer element 218 b, horizontally spaced apart from the plurality of strain gages 234 b, and a second additional plurality of strain gages (not shown) mounted on the outer, bottom surface of the second transducer element 218 b, and substantially vertically aligned with the first additional plurality of strain gages 234 c.

As explained above with regard to the first embodiment of the invention, it is highly advantageous that the first and second plate components 204, 206 only be connected to the protruding portions 236, 238, 240, 242 of the short force transducer beams 208, 210, 212 so as to ensure that the total load applied to the top surfaces 214, 216 of the plate components 204, 206 is only transmitted through the force transducer elements 218 a, 218 b, 218 c of the force transducer beams 208, 210, 212.

In the second embodiment of the invention, each short force transducer beam 208, 212 is provided with a respective support foot disposed near an outer end thereof. In FIG. 10, it can be seen that the first of the two short force transducer beams 208 is provided with one non-adjustable support foot 228 near the outer end thereof, whereas the first of the two short force transducer beams 212 is provided with one adjustable support foot 230 near the outer end thereof. Also, as depicted in FIG. 10, the second of the two short force transducer beams 212 is provided with a non-adjustable support foot 232, which is substantially the same as non-adjustable support foot 228. The second of the two force transducer beams 208 is not explicitly shown in FIG. 10, but it is provided with a non-adjustable support foot disposed near an outer end thereof, which is generally the same as non-adjustable support feet 228, 232. Like the dual force plate assembly 102 in the first embodiment of the invention, the dual force plate assembly 202 is designed to be installed on a floor of a building or on any other rigid surface. The adjustable support foot 230 facilitates the leveling of the dual force plate assembly 202 on an uneven surface.

C. Third Embodiment

A third embodiment of the dual force plate assembly is seen generally at 302 in FIGS. 12 and 13. In accordance with the third embodiment of the invention, the dual force plate assembly 302 for receiving a subject utilizes continuous force transducer beams 308 a, 308 b disposed on opposite lateral sides of the first and second plate components 304, 306, rather than force transducer beams disposed underneath the first and second plate components as described with regard to the first and second embodiments of the invention. As explained above in conjunction with the preceding two embodiments, the first plate component 304 has a top surface 312 that is configured to receive a first portion of a body of a subject. Similarly, the second plate component 306 has a top surface 314 that is configured to receive a second portion of a body of a subject. Also, similar to the first two embodiments described above, a narrow gap 320 is provided between the first plate component 304 and the second plate component 306 so as to prevent interaction between the two plate components 304, 306.

Advantageously, in a preferred embodiment, the dual force plate assembly 302 has an overall height that is significantly lower than conventional force plates used in balance assessment. This reduction in height is made possible, in part, by the mounting of the continuous force transducer beams 308 a, 308 b on the lateral sides of the first and second plate components 304, 306.

Referring to FIG. 12, it can be seen that each continuous force transducer beam 308 a, 308 b includes a plurality of force transducer elements 310 a, 310 b, 310 c disposed along the length thereof. Also, similar to the preceding two embodiments of the invention, each of the plurality of force transducer elements 310 a, 310 b, 310 c is provided with a respective aperture 316 a, 316 b, 316 c disposed therethrough. Moreover, as in the preceding embodiments, the outer transducer elements 310 a, 310 c measure the shear forces exerted on the first and second plate components 304, 306, respectively, whereas the centrally disposed transducer elements 310 b measure both the shear force and bending moment resulting from a load being applied to the first and second plate components 304, 306. Alternatively, rather than measuring both the shear force and bending moment, each centrally disposed transducer element 310 b can measure a first bending moment at a first location along the length of the transducer element 310 b and a second bending moment at a second location along the length of the transducer element 310 b, the first location being spaced apart from the second location.

Like the force transducer elements 112 a, 218 a described with regard to the first two embodiments of the invention, each first force transducer element 310 a is provided with a plurality of strain gages 318 a secured to the outer, top surface of its associated force transducer beam 308 a, 308 b, and substantially centered on the aperture 316 a (see FIG. 12). Also, similar to the force transducer elements 112 c, 218 c of the first two embodiments, each force transducer element 310 c is provided with a plurality of strain gages 318 d secured to the outer, top surface of its associated force transducer beam 308 a, 308 b, and substantially centered on the aperture 316 c. In addition, like the force transducer elements 112 b, 218 b of the first two embodiments of the invention, each force transducer element 310 b is provided with a plurality of strain gages 318 c secured to the outer, top surface of its associated force transducer beam 308 a, 308 b and substantially centered on the aperture 316 b, a first additional plurality of strain gages 318 b mounted on the outer, top surface of the second transducer element 310 b, horizontally spaced apart from the plurality of strain gages 318 c, and a second additional plurality of strain gages (not shown) mounted on the outer, bottom surface of the second transducer element 310 b, and substantially vertically aligned with the first additional plurality of strain gages 318 b.

Referring to FIGS. 12 and 13, it can be seen that each continuous force transducer beam 308 a, 308 b is fixedly attached to adjacent lateral sides of the first and second plate components 304, 306 using a plurality of screws 324. In particular, as best shown in the top view of FIG. 13, each force transducer beam 308 a, 308 b is attached to a respective centrally disposed protruding portion 322 on opposite lateral sides of the first plate component 304 and the second plate component 306. It is highly advantageously that the force transducer beams 308 a, 308 b only be connected to the centrally disposed protruding portions 322 of the first and second plate component 304, 306 so as to ensure that the total load applied to the top surfaces 312, 314 of the plate components 304, 306 is only transmitted through the force transducer elements 310 a, 310 b, 310 c on each side thereof. In FIG. 12, a total of four (4) screws 324 are used to connect each force transducer beam 308 a, 308 b to each plate component 304, 306. However, it is to be understood that the invention is not so limited. Rather, in other embodiments of the invention, more than four screws or less than four screws could be used to fixedly attach each force transducer beam 308 a, 308 b to each force plate component 304, 306. In yet other embodiments of the invention, the force transducer beams 308 a, 308 b could be connected to plate components 304, 306 by using different types of suitable adhesives (e.g., an adhesive designed for bonding metallic components to one another).

As best depicted in FIG. 12, the top surface 312 of the first plate component 304 and the top surface 314 of the second plate component 306 are both substantially aligned with the top surfaces of the transducer beams 308 a, 308 b in a preferred embodiment of the invention. This design feature enables the profile of the dual force plate assembly 302 to be minimized so that subjects are able to easily step on and off the dual force plate assembly 302. Also, it prevents the transducer beams 308 a, 308 b from posing a tripping hazard to subjects, as would be the case if the top surfaces of the transducer beams 308 a, 308 b were disposed above the top surfaces 312, 314 of the first and second plate components 304, 306. However, it is to be understood that the invention is not so limited. For example, in other embodiments of the invention, the top surfaces of the transducer beams 308 a, 308 b could be disposed below the top surfaces 312, 314 of the first and second plate components 304, 306.

In the third embodiment of the invention, each force transducer beam 308 a, 308 b is provided with respective support feet disposed at opposed longitudinal ends thereof. In FIG. 12, it can be seen that the first of the two transducer beams 308 a is provided with one non-adjustable support foot 326 near a first longitudinal end thereof and one adjustable support foot 328 near the other longitudinal end thereof. The bottom portion of the second of the two force transducer beams 308 b is not explicitly shown in FIG. 12, but it is provided with two (2) non-adjustable support feet disposed at opposed longitudinal ends thereof, both of which are generally the same as non-adjustable support foot 326. The dual force plate assembly 302 is designed to be installed on a floor of a building or on any other rigid surface. The adjustable support foot 328 facilitates the leveling of the dual force plate assembly 302 on an uneven surface.

D. Fourth Embodiment

A fourth embodiment of the dual force plate assembly is seen generally at 402 in FIGS. 14 and 15. In accordance with the fourth embodiment of the invention, the dual force plate assembly 402 for receiving a subject utilizes two sets of spaced apart, short transducer beams 408, 410, 412 disposed on opposite lateral sides of first and second plate components 404, 406, rather than the continuous transducer beams 308 a, 308 b described with respect to the third embodiment of the invention. As explained above in conjunction with the preceding three embodiments, the first plate component 404 has a top surface 416 that is configured to receive a first portion of a body of a subject. Similarly, the second plate component 406 has a top surface 418 that is configured to receive a second portion of a body of a subject. Also, similar to the first three embodiments described above, a narrow gap 426 is provided between the first plate component 404 and the second plate component 406 so as to prevent interaction between the two plate components 404, 406. Similar to the preceding embodiments described above, the short transducer beams 408, 410, 412 comprise respective transducer elements 414 a, 414 b, 414 c (which are formed by respective longitudinal segments of the force transducer beams 408, 410, 412) and respective apertures 420 a, 420 b, 420 c disposed therethrough. Also, as in the preceding embodiments, the outer transducer elements 414 a, 414 c measure the shear forces exerted on the first and second plate components 404, 406, respectively, whereas the centrally disposed transducer elements 414 b measure both the shear force and bending moment resulting from a load being applied to the first and second plate components 404, 406. Alternatively, rather than measuring both the shear force and bending moment, each centrally disposed transducer element 414 b can measure a first bending moment at a first location along the length of the transducer element 414 b and a second bending moment at a second location along the length of the transducer element 414 b, the first location being spaced apart from the second location.

Like the force transducer elements 112 a, 218 a, 310 a described with regard to the first three embodiments of the invention, the first force transducer element 414 a is provided with a plurality of strain gages 422 a secured to the outer, top surface of the force transducer beam 408 and substantially centered on the aperture 420 a (see FIG. 14). Also, similar to the force transducer elements 112 c, 218 c, 310 c of the first three embodiments, the force transducer element 414 c is provided with a plurality of strain gages 422 d secured to the outer, top surface of the force transducer beam 412 and substantially centered on the aperture 420 c. In addition, like the force transducer elements 112 b, 218 b, 310 b of the first three embodiments of the invention, the force transducer element 414 b is provided with a plurality of strain gages 422 c secured to the outer, top surface of the force transducer beam 410 and substantially centered on the aperture 420 b, a first additional plurality of strain gages 422 b mounted on the outer, top surface of the second transducer element 414 b, horizontally spaced apart from the plurality of strain gages 422 c, and a second additional plurality of strain gages (not shown) mounted on the outer, bottom surface of the second transducer element 414 b, and substantially vertically aligned with the first additional plurality of strain gages 422 b.

Now, referring to FIGS. 14 and 15, it can be seen that each first short transducer beam 408 is fixedly attached to the outer end portion of a respective centrally disposed protruding portion 424 on opposite lateral sides of the first plate component 404. Similarly, each third short transducer beam 412 is fixedly attached to the outer end portion of a respective centrally disposed protruding portion 424 on opposite lateral sides of the second plate component 406. Also, as depicted in FIGS. 14 and 15, each second short transducer beam 410 is fixedly attached to both the inner end portion of a respective centrally disposed protruding portion 424 on a lateral side of the first plate component 404 and the inner end portion of a respective centrally disposed protruding portion 424 on an adjacent lateral side of the second plate component 406. As described above with regard to the third embodiment, it is highly advantageous that the spaced apart, short transducer beams 408, 410, 412 only be connected to the first and second plate components 404, 406 by means of the centrally disposed protruding portions 424 so as to ensure that the total load applied to the top surfaces 416, 418 of the plate components 404, 406 is only transmitted through the force transducer elements 414 a, 414 b, 414 c.

In the fourth embodiment of the invention, each short force transducer beam 408, 412 is provided with a respective support foot disposed near an outer end thereof. In FIG. 14, it can be seen that the first of the two short force transducer beams 408 is provided with one non-adjustable support foot 428 near the outer end thereof, whereas the first of the two short force transducer beams 412 is provided with one adjustable support foot 430 near the outer end thereof. Also, while not explicitly shown in FIG. 14, the second of the two short force transducer beams 408 is provided with a non-adjustable support foot near an outer end thereof, which is substantially the same as non-adjustable support foot 428. Also, referring to FIG. 14, the second of the two short force transducer beams 412 is provided with a non-adjustable support foot near an outer end thereof, which is generally equivalent to non-adjustable support foot 428. Like the dual force plate assemblies described in the preceding embodiments of the invention, the dual force plate assembly 402 is designed to be installed on a floor of a building or on any other rigid surface. The adjustable support foot 430 facilitates the leveling of the dual force plate assembly 402 on an uneven surface.

E. Fifth Embodiment

A fifth embodiment of the dual force plate assembly is seen generally at 502 in FIG. 16. In accordance with the fifth embodiment of the invention, the dual force plate assembly 502 for receiving a subject utilizes three plate components 504, 506, 508, rather than two plate components as employed in the previous embodiments of the invention. Two sets of spaced apart, short transducer beams 510, 512, 514, 516 are disposed underneath, and near opposite sides of, the first, second, and third plate components 504, 506, 508. As depicted in FIG. 16, each short transducer beam 510 has a top protruding portion 528 that is fixedly attached to the bottom surface of the first plate component 504. Similarly, each oppositely disposed, short transducer beam 516 has a top protruding portion 538 that is fixedly attached to the bottom surface of the third plate component 508. Each short transducer beam 512, which extends below a continuous gap 540 between the first and second plate components 504, 506, comprises a first protruding portion 530 that is fixedly attached to the bottom surface of the first plate component 504 and second protruding portion 532 that is fixedly attached to the bottom surface of the second plate component 506. Similarly, each short transducer beam 514, which extends below a continuous gap 542 between the second and third plate components 506, 508, comprises a first protruding portion 534 that is fixedly attached to the bottom surface of the second plate component 506 and second protruding portion 536 that is fixedly attached to the bottom surface of the third plate component 508. Like the preceding embodiments described above, the short transducer beams 510, 512, 514, 516 comprise respective transducer elements 524 a, 524 b, 524 c, 524 d and respective apertures 526 a, 526 b, 526 c, 526 d disposed therethrough. Also, similar to that described with regard to the preceding embodiments, the outer transducer elements 524 a, 524 d measure the shear forces exerted on the first and third plate components 504, 508, respectively, whereas the centrally disposed transducer elements 524 b measure both the shear force and bending moment resulting from a load being applied to the first and second plate components 504, 506 and the centrally disposed transducer elements 524 c measure both the shear force and bending moment resulting from a load being applied to the second and third plate components 506, 508. Alternatively, rather than measuring both the shear force and bending moment, each centrally disposed transducer element 524 b, 524 c can measure a first bending moment at a first location along the length of the transducer element 524 b, 524 c and a second bending moment at a second location along the length of the transducer element 524 b, 524 c, the first location being spaced apart from the second location.

As explained above with regard to the preceding embodiments of the invention, it is highly advantageous that the first, second, and third plate components 504, 506, 508 only be connected to the protruding portions 528, 530, 532, 534, 536, 538 of the short force transducer beams 510, 512, 514, 516 so as to ensure that the total load applied to the top surfaces 518, 520, 522 of the plate components 504, 506, 508 is only transmitted through the force transducer elements 524 a, 524 b, 525 c, 524 b of the force transducer beams 510, 512, 514, 516.

In the fifth embodiment of the invention, each short force transducer beam 510 is provided with a non-adjustable support foot 544 near the outer longitudinal end thereof. One of the two short force transducer beams 516 is also provided with a non-adjustable support foot 544 near the outer longitudinal end thereof (not visible in FIG. 16), whereas the other of the two short force transducer beams 516 is provided with an adjustable support foot 546 to permit the leveling of the dual force plate assembly 502 on an uneven surface.

F. Computations Performed by the Data Acquisition/Data Processing Device 104

Now, the manner in which the data acquisition/data processing device 104 calculates the applied forces and the center of pressure for each of the subject's two feet will be described in detail. The center of pressure for each foot of the subject comprises the x and y coordinates of the point of application of the force applied to the measurement surface by that foot. During the balance assessment of a patient, the variation in the center of pressure (i.e., the sway of the patient) is monitored so as to determine the overall stability of that patient. Initially, referring to FIGS. 17A-17D, the mathematical determination of the x-coordinates for each foot of the subject will be explained. Then, with reference to FIG. 18, the determination of the y-coordinates for each foot of the subject will be described.

FIG. 17A depicts a side view of a dual force plate assembly of a dual force plate system, wherein the unknown parameters to be determined are diagrammatically depicted thereon. The first set of unknown parameters comprises: (i) the force F_(L) applied to the first measurement surface of the first force plate by the left foot of the subject, and (ii) the force F_(R) applied to the second measurement surface of the second force plate by the right foot of the subject. The second set of unknown parameters comprises: (i) the distance x_(L) measured from a reference point at the outer edge of the first force plate to the point of application of the force F_(L) exerted on the first measurement surface by the left foot of the subject, and (ii) the distance x_(R) measured from a reference point at the outer edge of the first force plate to the point of application of the force F_(R) exerted on the second measurement surface by the right foot of the subject (i.e., the x-coordinates of the center of pressure for each foot of the subject). Thus, initially there are a total of four unknown parameters that need to be determined.

In FIG. 17A, the dual force plate assembly is diagrammatically depicted as being supported on simple supports, which are otherwise known as knife-edge supports. This model is appropriate for the typical arrangement of the dual force plate assembly in which the feet of the assembly are simply resting on the surface of the floor, and thus, there is no moment reaction at the supports. However, it is to be understood that the invention is not so limited. Rather, in other embodiments of the invention, the feet of the dual force plate assembly are fixedly attached to the floor, and therefore, the connections between the force plate assembly and the floor are capable of transmitting moments. The mathematical analysis for such an arrangement would be similar to that provided below except that non-zero moments would be present at each support.

In FIG. 17B, a free diagram body of the dual force plate assembly is shown in order to graphically illustrate measured parameters of the system. Referring to this figure, it can be seen that the dual force plate assembly is being modeled as one continuous, simply supported beam. The dual force plate assembly can be accurately modeled as a single beam because the center transducer beams, each of which operatively connects the first plate to the second plate, are fixedly attached to the bottom surfaces of the first and second plates. Thus, even though separate components are utilized in the actual assembly, the dual force plate operates as if it is a single structure. As depicted in FIG. 17B, the shear force R_(A) acting on the left end of the assembly is sensed by a first force transducer element, while the shear force R_(C) acting on the right end of the assembly is measured by a second force transducer element. The third force transducer element, which is disposed on the center transducer beam, measures both the shear force R_(B) and the moment M_(B) (i.e., it measures the load transferred between the first and second plates).

Now that both the unknown parameters and the measured parameters of the dual force plate system have been defined, the mathematical equations for determining the unknown parameters of the system can be formulated. The forces exerted on the first and second force plates by the respective left and right feet of the subject are described by the following two equations: F _(L) =R _(A) −R _(B)  (1) F _(R) =R _(B) +R _(C)  (2)

where:

-   -   F_(L): force exerted on the surface of the first force plate by         the left foot of the subject;     -   F_(R): force exerted on the surface of the second force plate by         the right foot of the subject;     -   R_(A): shear force measured by the first force transducer         element;     -   R_(B): shear force measured by the third force transducer         element (i.e. between the two plates); and     -   R_(C): shear force measured by the second force transducer         element.         Thus, applied forces can be obtained by plugging the shear         forces R_(A), R_(B), and R_(C), which are measured by the force         transducer elements, into equations (1) and (2) and then,         solving for forces F_(L) and F_(R).

Alternatively, if each centrally disposed transducer element measures a first and second bending moment M₁, M₂, rather than the shear force and a single bending moment, then the shear force R_(B) can be determined by utilizing the following equation:

$\begin{matrix} {R_{B} = \frac{\left( {M_{2} - M_{1}} \right)}{d}} & (3) \end{matrix}$

where:

-   -   M₁: first bending moment measured at a first location along the         length of the third transducer element (e.g., see FIG. 17A,         centrally located transducer beam);     -   M₂: second bending moment measured at a second location along         the length of the third transducer element (e.g., see FIG. 17A,         centrally located transducer beam); and     -   d: distance between the first location and the second location         along the length of the third transducer element (e.g., see FIG.         17A, centrally located transducer beam).         Then, the applied forces F_(L), F_(R) can be determined from         equations (1) and (2) by using the computed shear force R_(B)         together with the measured shear forces R_(A) and R_(C).

Next, turning to the shear diagram depicted in FIG. 17C, the moment M_(B) is equal to the area under the shear force curves as follows:

$\begin{matrix} {M_{B} = {\left( {R_{B} \cdot \left( \frac{L}{2} \right)} \right) + \left( {F_{L} \cdot x_{L}} \right)}} & (4) \end{matrix}$

where:

-   -   M_(B): moment about point B;     -   R_(B): shear force measured by the third force transducer         element (i.e. between the two plates) or computed;     -   L: overall length of the dual force plate assembly (i.e.,         combined length of the first and second force plates);     -   F_(L): force exerted on the surface of the first force plate by         the left foot of the subject; and     -   x_(L): distance measured from a reference point at the outer         edge of the first force plate to the point of application of the         force F_(L) exerted on the first measurement surface by the left         foot of the subject;         The moment M_(B) is graphically depicted in the moment diagram         of FIG. 17D. Then, in order to solve for the desired unknown         quantity, the terms of equation (4) are rearranged as follows:

$\begin{matrix} {x_{L} = \frac{M_{B} - \left( {R_{B} \cdot \left( \frac{L}{2} \right)} \right)}{F_{L}}} & (5) \end{matrix}$

Similarly, the unknown coordinate x_(R) can be determined from the following moment balance equation, wherein the moments are summed about point A in a clockwise direction: (x _(L) ·F _(L))+(x _(R) ·F _(R))−(L·R _(C))=0  (6)

where:

-   -   x_(R): distance measured from a reference point at the outer         edge of the first force plate to the point of application of the         force F_(R) exerted on the second measurement surface by the         right foot of the subject.         Then, in order to solve for the desired unknown quantity x_(R),         the terms of equation (6) are rearranged as follows:

$\begin{matrix} {x_{R} = \frac{\left( {L \cdot R_{C}} \right) - \left( {x_{L} \cdot F_{L}} \right)}{F_{R}}} & (7) \end{matrix}$

Once the forces F_(L) and F_(R) and the x-coordinates of the center of pressure for each foot of the subject have been determined in the manner delineated above, a computational method that can be carried out by the data acquisition/data processing device 104 to compute the y-coordinates of the center of pressure for each foot of the subject will be explained with reference to the three-dimensional (3-D) free body diagram/shear diagram of FIG. 18. When broken down into their constituent components, the forces exerted on the first and second force plates by the respective left and right feet of the subject are described by the following two equations: F _(L) =F _(L1) +F _(L2)  (8) F _(R) =R ^(R1) +R _(R2)  (9)

where:

-   -   F_(L): force exerted on the surface of the first force plate by         the left foot of the subject;     -   F_(L1): first constituent component of the force exerted on the         surface of the first force plate by the left foot of the         subject;     -   F_(L2): second constituent component of the force exerted on the         surface of the first force plate by the left foot of the         subject;     -   F_(R): force exerted on the surface of the second force plate by         the right foot of the subject;     -   F_(R1): first constituent component of the force exerted on the         surface of the second force plate by the right foot of the         subject; and     -   F_(R2): second constituent component of the force exerted on the         surface of the second force plate by the right foot of the         subject.

Then, the unknown coordinate y_(L) can be determined from the following moment balance equation, wherein the moments are summed about a point on a first side S1 of the first force plate in a clockwise direction: (F _(L) ·y _(L))−(F _(L2) ·W)=0  (10)

where:

-   -   y_(L): distance measured from a reference point on the first         side S1 of the first force plate to the point of application of         the force F_(L) exerted on the measurement surface by the left         foot of the subject; and     -   W: width of the dual force plate assembly.

Next, in order to solve for the desired unknown quantity y_(L), the terms of equation (10) are rearranged as follows:

$\begin{matrix} {y_{L} = {W \cdot \left( \frac{F_{L\; 2}}{F_{L}} \right)}} & (11) \end{matrix}$

Following a similar procedure, the last unknown parameter y_(R) can be determined from the following moment balance equation, wherein the moments are summed about a point on a first side S1 of the second force plate in a clockwise direction: (F _(R) ·y _(R))−(F _(R2) ·W)=0  (12)

where:

-   -   y_(R): distance measured from a reference point on the first         side S1 of the second force plate to the point of application of         the force F_(R) exerted on the second measurement surface by the         right foot of the subject.

Next, in order to solve for the desired unknown quantity y_(R), the terms of equation (12) are rearranged as follows:

$\begin{matrix} {y_{R} = {W \cdot \left( \frac{F_{R\; 2}}{F_{R}} \right)}} & (13) \end{matrix}$

Therefore, all of the unknown parameters of the dual force plate system are mathematically determined in the manner explained above by the data acquisition/data processing device 104. In a preferred embodiment of the invention, the data acquisition/data processing device 104 is specially programmed to perform all of these abovedescribed calculations.

While the exemplary force plate systems explained above employ forces plate assemblies 102, 202, 302, 402, 502 that are configured to receive a subject in an upright position, it is to be understood that the invention is not so limited. Rather, the present invention can be practiced with a force plate assembly that measures the forces exerted by the limbs of a subject that is disposed in a position other than an upright position, such as subject in a substantially horizontal position. For example, a dual force assembly could be mounted on a vertical surface (e.g., the vertical side of a swimming pool) to measure the substantially horizontal forces exerted on the vertical surface by the arms and/or the legs of the subject.

Although the invention has been shown and described with respect to a certain embodiment or embodiments, it is apparent that this invention can be embodied in many different forms and that many other modifications and variations are possible without departing from the spirit and scope of this invention. For example, in some embodiments of the invention, a virtual reality system is provided in conjunction with the dual force plate system so that the subject can be tested while experiencing a variety of different simulated scenarios.

While exemplary embodiments have been described herein, one of ordinary skill in the art will readily appreciate that the exemplary embodiments set forth above are merely illustrative in nature and should not be construed as to limit the claims in any manner. Rather, the scope of the invention is defined only by the appended claims and their equivalents, and not, by the preceding description. 

The invention claimed is:
 1. A dual force plate system having two independent measurement surfaces, the dual force plate system comprising: a first plate component having a first measurement surface for receiving a first portion of a body of a subject, a first opposed surface that is disposed generally opposite to the first measurement surface, and a plurality of lateral surfaces that extend between the first measurement surface and the first opposed surface; a second plate component having a second measurement surface for receiving a second portion of the body of the subject, a second opposed surface that is disposed generally opposite to the second measurement surface, and a plurality of lateral surfaces that extend between the second measurement surface and the second opposed surface; a first force transducer element operatively coupled to either the first opposed surface of the first plate component or to one of the lateral surfaces of the first plate component, the first force transducer element configured to output at least one first quantity that is representative of a load being applied to the first measurement surface; a second force transducer element operatively coupled to either the second opposed surface of the second plate component or to one of the lateral surfaces of the second plate component, the second force transducer element configured to output at least one second quantity that is representative of a load being applied to the second measurement surface; and a third force transducer element operatively coupled to either the first opposed surface of the first plate component and the second opposed surface of the second plate component, or to one of the lateral surfaces of the first plate component and one of lateral surfaces of second plate component, the third force transducer element configured to output at least one third quantity that is representative of a load being transferred between the first plate component and the second plate component; wherein the first force transducer element is in the form of a first discrete transducer beam, the second force transducer element is in the form of a second discrete transducer beam, and the third force transducer element is in the form of a third discrete transducer beam; wherein the first and third discrete transducer beams are spaced apart from the second discrete transducer beam in a longitudinal direction thereof; and wherein the first, second, and third discrete transducer beams are disposed in a spaced apart relationship along the first and second opposed surfaces of the first and second plate components, or along two adjacent lateral surfaces of the first and second plate components.
 2. The dual force plate system according to claim 1, wherein either the first and third force transducer elements are both operatively coupled to the first opposed surface of the first plate component, or the first and third force transducer elements are both operatively coupled to the same lateral surface of the first plate component.
 3. The dual force plate system according to claim 2, wherein either the second and third force transducer elements are both operatively coupled to the second opposed surface of the second plate component, or the second and third force transducer elements are both operatively coupled to the same lateral surface of the second plate component.
 4. The dual force plate system according to claim 3 further comprising: a fourth force transducer element laterally spaced apart from the first force transducer element, the fourth force transducer element operatively coupled to either the first opposed surface of the first plate component or to another one of the lateral surfaces of the first plate component, the fourth force transducer element configured to output at least one fourth quantity that is representative of a load being applied to the first measurement surface; a fifth force transducer element laterally spaced apart from the second force transducer element, the fifth force transducer element operatively coupled to either the second opposed surface of the second plate component or to another one of the lateral surfaces of the second plate component, the fifth force transducer element configured to output at least one fifth quantity that is representative of a load being applied to the second measurement surface; and a sixth force transducer element laterally spaced apart from the third force transducer element, the sixth force transducer element operatively coupled to either the first opposed surface of the first plate component and the second opposed surface of the second plate component, or to another one of the lateral surfaces of the first plate component and another one of lateral surfaces of second plate component, the sixth force transducer element configured to output at least one sixth quantity that is representative of a load being transferred between the first plate component and the second plate component.
 5. The dual force plate system according to claim 4, wherein the first, second, and third force transducer elements are generally symmetrically arranged with respect to the fourth, fifth, and sixth force transducer elements.
 6. The dual force plate system according to claim 1, wherein the first force transducer element is mounted in a cantilevered manner from the first plate component and the second force transducer element is mounted in a cantilevered manner from the second plate component.
 7. The dual force plate system according to claim 1 further comprising a data processing device operatively coupled to the first force transducer element, the second force transducer element, and the third force transducer element, the data processing device configured to receive the first, second, and third quantities that are representative of the loads being applied to the first measurement surface, the second measurement surface, and transferred between the first and second plate components, respectively, and to convert the first, second, and third quantities into output loads.
 8. The dual force plate system according to claim 1, wherein the first force transducer element, the second force transducer element, and the third force transducer element each comprise an aperture disposed therein and a plurality of strain gages disposed on an outer surface thereof, the outer surface of each force transducer element on which the plurality of strain gages are disposed being generally opposite to an inner surface of each aperture.
 9. The dual force plate system according to claim 8, wherein a support foot having a longitudinal axis is disposed on both the first force transducer element and the second force transducer element, the longitudinal axis of each support foot being disposed substantially perpendicular to the extending direction of a respective aperture in the first force transducer element and the second force transducer element.
 10. The dual force plate system according to claim 8, wherein the third force transducer element further comprises an additional plurality of strain gages disposed on opposed outer surfaces thereof for sensing mechanical strain resulting from both tension and compression.
 11. The dual force plate system according to claim 1, wherein the first force transducer element and the second force transducer element each have a protruding portion disposed on an outer surface thereof, and wherein the first and second force transducer elements are respectively coupled to the first and second plate components by means of their respective protruding portions.
 12. The dual force plate system according to claim 11, wherein the third force transducer element has first and second protruding portions disposed on an outer surface thereof, the first protruding portion being operatively coupled to the first opposed surface of the first plate component, the second protruding portion being spaced apart from the first protruding portion and being operatively to the second opposed surface of the second plate component.
 13. The dual force plate system according to claim 1, wherein the first force transducer element is operatively coupled to one of the lateral surfaces of the first plate component and the second force transducer element is operatively coupled to one of the lateral surfaces of the second plate component, wherein the lateral surface of the first plate component to which the first force transducer element is operatively coupled, and the lateral surface of the second plate component to which the second force transducer element is operatively coupled, each have a centrally disposed protruding portion; and wherein the first force transducer element is operatively coupled to the centrally disposed protruding portion of the first plate component, and the second force transducer element is operatively coupled to the centrally disposed protruding portion of the second plate component.
 14. The dual force plate system according to claim 13, wherein the third force transducer element is operatively coupled to the centrally disposed protruding portion of the first plate component and the centrally disposed protruding portion of the second plate component.
 15. The dual force plate system according to claim 1, wherein the first plate component and second plate component are both constructed from a material or a composite structure having a high stiffness value such that the natural frequency of the dual force plate system is maximized and the first and second plate components are capable of withstanding the weight of the subject.
 16. The dual force plate system according to claim 1, wherein a gap is provided between the first plate component and the second plate component so as to prevent interaction between the two plate components.
 17. The dual force plate system according to claim 1, wherein the first force transducer element and the second force transducer element each comprise an elastically deformable structural member and a plurality of strain gages, the strain gages being used to measure the deformation of the elastically deformable structural member due to shear.
 18. The dual force plate system according to claim 1, wherein the third force transducer element comprises an elastically deformable structural member, a first plurality of strain gages disposed on a first side of the elastically deformable structural member, and a second plurality of strain gages disposed on a second side of the elastically deformable structural member that is opposite to the first side, the first and second pluralities of strain gages being used to measure the deformation of the elastically deformable structural member due to bending.
 19. A dual force plate system having two independent measurement surfaces, the dual force plate system comprising: a first plate component having a first measurement surface for receiving a first portion of a body of a subject, a first opposed surface that is disposed generally opposite to the first measurement surface, and a plurality of lateral surfaces that extend between the first measurement surface and the first opposed surface; a second plate component having a second measurement surface for receiving a second portion of the body of the subject, a second opposed surface that is disposed generally opposite to the second measurement surface, and a plurality of lateral surfaces that extend between the first measurement surface and the second opposed surface, the second plate component being spaced apart from the first plate component by a gap; a first force transducer element operatively coupled to either the first opposed surface of the first plate component or to one of the lateral surfaces of the first plate component, the first force transducer element configured to output at least one first quantity that is representative of a load being applied to the first measurement surface; a second force transducer element operatively coupled to either the second opposed surface of the second plate component or to one of the lateral surfaces of the second plate component, the second force transducer element configured to output at least one second quantity that is representative of a load being applied to the second measurement surface; a third force transducer element operatively coupled to either the first opposed surface of the first plate component and the second opposed surface of the second plate component, or to one of the lateral surfaces of the first plate component and one of lateral surfaces of second plate component, the third force transducer element extending across the gap between the first plate component and the second plate component, the third force transducer element configured to output at least one third quantity that is representative of a load being transferred between the first plate component and the second plate component; and a data processing device operatively coupled to the first force transducer element, the second force transducer element, and the third force transducer element, the data processing device configured to receive the first, second, and third quantities that are representative of the loads being applied to the first measurement surface, the second measurement surface, and transferred between the first and second plate components, respectively, and to convert the first, second, and third quantities into separate output loads for each of the first plate component and the second plate component.
 20. A force measurement assembly having two measurement surfaces, the force measurement assembly comprising: a first component having a first measurement surface configured to receive a first portion of a body of a subject or a first object exerting a load thereon, the first component being structurally supported by a first load measuring device; a second component having a second measurement surface configured to receive a second portion of the body of the subject or a second object exerting a load thereon, the second component being structurally supported by a second load measuring device and being spaced apart from the first component by a gap; a third load measuring device operatively coupled to both the first component and the second component, the third load measuring device extending across the gap between the first component and the second component; wherein the first load measuring device is configured to output at least one first quantity that is representative of the load being applied to the first measurement surface, the second load measuring device is configured to output at least one second quantity that is representative of the load being applied to the second measurement surface, and the third load measuring device is configured to output at least one third quantity that is representative of a load being transferred between the first component and the second component; and a data processing device operatively coupled to the first load measuring device, the second load measuring device, and the third load measuring device, the data processing device configured to receive the first, second, and third quantities that are representative of the loads being applied to the first measurement surface, the second measurement surface, and transferred between the first and second components, respectively, and to convert the first, second, and third quantities into separate output loads for each of the first component and the second component.
 21. A force plate system having three or more independent measurement surfaces, the force plate system comprising: a first outer plate component having a first measurement surface, a first opposed surface that is disposed generally opposite to the first measurement surface, and a plurality of lateral surfaces that extend between the first measurement surface and the first opposed surface; a second outer plate component having a second measurement surface, a second opposed surface that is disposed generally opposite to the second measurement surface, and a plurality of lateral surfaces that extend between the second measurement surface and the second opposed surface; one or more inner plate components that are disposed between the first outer plate component and the second outer plate component, each inner plate component having a measurement surface, an opposed surface that is disposed generally opposite to the measurement surface, and a plurality of lateral surfaces that extend between the measurement surface and the opposed surface, each inner plate component which is disposed adjacent to at least one of the first outer plate component and the second outer plate component being spaced apart from the at least one of the first outer plate component and the second outer plate component by a respective gap; a first outer force transducer element operatively coupled to either the first opposed surface of the first outer plate component or to one of the lateral surfaces of the first outer plate component, the first outer force transducer element configured to output at least one first quantity that is representative of a load being applied to the first measurement surface; a second outer force transducer element operatively coupled to either the second opposed surface of the second outer plate component or to one of the lateral surfaces of the second outer plate component, the second outer force transducer element configured to output at least one second quantity that is representative of a load being applied to the second measurement surface; and a plurality of inner force transducer elements operatively coupling the one or more inner plate components to either the first and second opposed surfaces of the first and second outer plate components, or to lateral surfaces of the first and second outer plate components, the plurality of inner forces transducer elements configured to output a plurality of quantities that are representative of loads being transferred between the one or more inner plate components and the first and second outer plate components, and the plurality of inner force transducer elements extending across the respective gaps between each inner plate component and the at least one of the first outer plate component and the second outer plate component.
 22. A dual force plate system having two independent measurement surfaces, the dual force plate system comprising: a first plate component having a first measurement surface for receiving a first portion of a body of a subject, a first opposed surface that is disposed generally opposite to the first measurement surface, and a plurality of lateral surfaces that extend between the first measurement surface and the first opposed surface; a second plate component having a second measurement surface for receiving a second portion of the body of the subject, a second opposed surface that is disposed generally opposite to the second measurement surface, and a plurality of lateral surfaces that extend between the second measurement surface and the second opposed surface, the second plate component being spaced apart from the first plate component by a gap; a first force transducer element operatively coupled to either the first opposed surface of the first plate component or to one of the lateral surfaces of the first plate component, the first force transducer element configured to output at least one first quantity that is representative of a load being applied to the first measurement surface; a second force transducer element operatively coupled to either the second opposed surface of the second plate component or to one of the lateral surfaces of the second plate component, the second force transducer element configured to output at least one second quantity that is representative of a load being applied to the second measurement surface; and a third force transducer element operatively coupled to either the first opposed surface of the first plate component and the second opposed surface of the second plate component, or to one of the lateral surfaces of the first plate component and one of lateral surfaces of second plate component, the third force transducer element extending across the gap between the first plate component and the second plate component, the third force transducer element configured to output at least one third quantity that is representative of a load being transferred between the first plate component and the second plate component; wherein the first force transducer element, the second force transducer element, and the third force transducer element are each part of a continuous beam force transducer assembly having a longitudinal axis, the first, second and third force transducer elements being spaced apart along the longitudinal axis of the continuous beam force transducer assembly and each of the first, second and third force transducer elements intersecting the longitudinal axis of the continuous beam force transducer assembly; and wherein the continuous beam force transducer assembly extends substantially the combined length of the first and second opposed surfaces of the first and second plate components, or the combined length of the lateral surfaces of the first and second plate components, to which the first and second force transducer elements are respectively coupled. 